­ 

COMMON ROCKS

(Igneous, Sedimentary, Metamorphic)

 

IGNEOUS ROCKS

Igneous rocks form by the cooling & crystallization of hot, molten rock (magma & lava).  If this happens at or near the land surface, or on the seafloor, they are extrusive igneous rocks.  If this happens deep underground, they are intrusive igneous rocks.

Most igneous rocks have a crystalline texture, but some are clastic, vesicular, frothy, or glassy.

 

 

GRANITE      BASALT & OLIVINE BASALT           ANDESITE

 

RHYOLITE                  GABBRO                         DIORITE

 

PORPHYRITIC GRANITE             PUMICE

 

PORPHYRITIC RHYOLITE          SCORIA

 

PORPHYRITIC BASALT  VESICULAR BASALT

 

OBSIDIAN           SNOWFLAKE OBSIDIAN

 

VOLCANIC BRECCIA       VOLCANIC TUFF

 

ANORTHOSITE                         PERIDOTITE

 

QUARTZ  MONZONITE

 

 

Classification of igneous rocks (according to the British Geological Survey) (662 kb pdf)

 

 

SEDIMENTARY ROCKS

Sedimentary rocks form by the solidification of loose sediments.  Loose sediments become hard rocks by the processes of deposition, burial, compaction, dewatering, and cementation.

If the sediments are derived from weathering & erosion of any previously existing rocks, you've got siliciclastic sedimentary rocks.

If the sediments are derived from once-living organisms (plants, animals, micro-organisms), you've got biogenic sedimentary rocks.

If the sediments formed by inorganic chemical means, you've got a chemical sedimentary rock.

Most sedimentary rocks have clastic textures, but some are crystalline.

 

CONGLOMERATE             BRECCIA            ARKOSE

 

SANDSTONE & GRAYWACKE SILTSTONE                 SHALE

 

LIMESTONE      COQUINA       CHALK

 

OOLITIC LIMESTONE            ONCOLITIC LIMESTONE

 

CHERT                BANDED IRON FORMATION            PEAT

 

LIGNITE COAL      CANNEL COAL BITUMINOUS COAL

 

DOLOSTONE          ROCK SALT        ROCK GYPSUM

 

DIATOMITE         OIL SHALE              TAR SANDSTONE

 

BAUXITE                PHOSPHORITE

 

 

Classification of sedimentary rocks (according to the British Geological Survey) (459 kb pdf)

 

 

METAMORPHIC ROCKS

Metamorphic rocks result from intense alteration of any previously existing rocks by heat and/or pressure and/or chemical change.  This can happen as a result of regional metamorphism (large-scale tectonic events, such as continental collision or subduction), burial metamorphism (super-deep burial), contact metamorphism (by the heat & chemicals from nearby magma or lava), hydrothermal metamorphism (by superheated groundwater), shear metamorphism (in or near a fault zone), or shock metamorphism (by an impact event).

Many metamorphic rocks have a foliated texture, but some are crystalline or glassy.

 

MARBLE            QUARTZITE       GREENSTONE            EPIDOTITE

 

DOLOMITIC MARBLE       SOAPSTONE       ECLOGITE

 

SLATE       PHYLLITE       SCHIST       GNEISS             MIGMATITE

 

GRANULITE       CHARNOCKITE       TECTONITE                 SKARN

 

ANTHRACITE COAL METACHERT       SERPENTINITE

 

METACONGLOMERATE             TECTONIC BRECCIA

 

HORNFELS       GARNETITE

 

 

Classification of metamorphic rocks (according to the British Geological Survey) (260 kb pdf)

 

 

 

Home page